Mast head for a dragline

ABSTRACT

A mast head assembly for a dragline comprises an elongated body for connecting to a mast of a dragline. The elongated body includes side plates on opposite sides of the body. The side plates have suspension lugs and chord and lacing stubs for attaching cables from the mast head to the boom of a dragline. At least one of the cord stubs is located above and to the rear of a first chord stub. The chord and lacing stubs are positioned on the side plates so that the maximum stress in the mast head assembly is where the chord stub connects to the original chord. The highest remaining stress is located at the point where the upper/rear chord stub connects to the original chord.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Application No. 61/623,949, which was filed on Apr. 13, 2012, and International Application no. PCT/US2012/035646, which was filed on Apr. 27, 2012, both of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to a mast head assembly for a dragline.

BACKGROUND

Draglines are an important excavating tool used in many surface mining operations worldwide. These highly productive machines operate 24 hours a day, seven days a week and are able to reach depths of 79.8 m (262 ft) with capacities up to 116.2 m³ (152 yd³). Offering the lowest material removal cost per tonne (ton) and an average operating life of 40 years, draglines are the most productive and versatile machine in the industry.

Draglines, the largest single-bucket excavators in existence today, are used primarily for the removal of overburden in long-life surface coal mines.

The mast head box on draglines have been problematic after several years of use, and generally require lengthy repairs followed by increasingly frequent cracking. Instead of performing frequent repairs, the disclosed device is a new mast head box design.

SUMMARY

The disclosed device is a mast head assembly for a dragline. The mast head assembly comprises an elongated body for connecting to a mast of a dragline. The elongated body includes side plates on opposite sides of the body. The side plates have suspension lugs and chord and lacing stubs for attaching cables from the mast head to the boom of a dragline. At least one of the cord stubs is located above and to the rear of a first chord stub. The chord and lacing stubs are positioned on the side plates so that the maximum stress in the mast head assembly is where the chord stub connects to the original chord. The highest remaining stress is located at the point where the upper/rear chord stub connects to the original chord.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements, in which:

FIG. 1 is a perspective view of an original design for a mast head assembly.

FIG. 2 is a perspective view of a mast head assembly of the present disclosure, according to an exemplary embodiment.

FIG. 3 is an image of a first location of a mast head assembly (i.e., Location 1), including a connection between a chord and a mast head box.

FIG. 4 is an image of a third and fourth location of a mast head assembly (i.e., Locations 3 and 4), including a rear plate of the mast head box.

FIG. 5 is another image of the fourth location of the mast head assembly (i.e., Location 4), including the rear plate of the mast head box.

FIG. 6 is an image of an eighth location of a mast head assembly (i.e., Location 8), including a top portion of an intermediate lug.

FIG. 7 is an image of the mast head assembly near Location 8, including a side of an intermediate lug plate.

FIG. 8 is another image of the mast head assembly near Location 8, including a top portion of the intermediate lug plate.

FIG. 9 is an illustration of a beam analysis model for a mast, according to an exemplary embodiment.

FIG. 10 is an illustration of a pin and link part model for a mast head assembly, according to an exemplary embodiment.

FIG. 11 is an illustration of a detailed analysis model for a mast head assembly, according to an exemplary embodiment.

FIG. 12 is another illustration of a beam analysis model for a mast, including various cut plane nodes, according to an exemplary embodiment.

FIG. 13 is a perspective view of a mast head assembly with constraints applied, according to an exemplary embodiment.

FIG. 14 is a perspective view of contact surfaces on the mast head assembly, according to an exemplary embodiment.

FIG. 15 is a perspective view of a mast head assembly, including maximum and minimum load cases for the mast head assembly, according to an exemplary embodiment.

FIG. 16 is an illustration of a meshed beam analysis model for a mast, according to an exemplary embodiment.

FIG. 17 is an illustration of a meshed beam analysis model for an original design of the mast head assembly.

FIG. 18 is an illustration of a meshed beam analysis model for a mast head assembly, according to an exemplary embodiment.

FIG. 19 is an illustration of a deflection analysis model for the mast head assembly according to a maximum load (50×).

FIG. 20 is an illustration of a deflection analysis model for the mast head assembly according to a minimum load (100×).

FIG. 21 is an illustration of a stress analysis model for the mast head assembly according to a maximum load.

FIG. 22 is a perspective view of high stress locations on the original design of the mast head assembly.

FIG. 23 is an illustration of high stress locations on the original design of the mast head assembly.

FIG. 24 is another illustration of high stress locations on the original design of the mast head assembly.

FIG. 25 is a perspective view of high stress locations on the mast head assembly, according to an exemplary embodiment.

FIG. 26 is an illustration of high stress locations on the mast head assembly, according to an exemplary embodiment.

FIG. 27 is another illustration of high stress locations on the mast head assembly, according to an exemplary embodiment.

FIG. 28 is an illustration of a first principal stress (tension) for Load Case 1 of the mast head assembly, according to an exemplary embodiment.

FIG. 29 is an illustration of a third principal stress (compression) for Load Case 1 of the mast head assembly, according to an exemplary embodiment.

FIG. 30 is an illustration of a chord member having a first wall thickness, according to an exemplary embodiment.

FIG. 31 is an illustration of a chord member having a second wall thickness, according to an exemplary embodiment.

FIG. 32 is an illustration of a chord member having a third wall thickness, according to an exemplary embodiment.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplary embodiments in detail, it should be understood that the present application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting.

The disclosed information and analysis was done on a model 1570W dragline manufactured by Bucyrus, now Caterpillar. This model had the following general capacities: bucket capacities—48 to 61 m³ (63 to 80 yd³); boom lengths—94 to 105 m (310 to 345 ft); maximum allowable load—142,900 to 181,400 kg (315,000 to 400,000 lbs); maximum working weight—3,630,000 kg (8,000,000 lbs). However, the disclosed device has general applicability to other draglines as well.

After an initial analysis it was deemed necessary to perform an entire beam analysis of the mast in order to map displacements and rotations to the smaller, more detailed model. To provide an accurate and fair comparison, the original and the upgrade were analyzed with identical boundary conditions and loads. The loads were determined by reviewing historical boom and mast analysis models. Additionally, both designs were analyzed at the maximum and minimum loads that would be experienced while digging to obtain a stress range for fatigue analysis.

As evident in FIGS. 1 and 2, the upgrade design 100 extends further down the mast, has a cleaner design, fewer components, and thicker plating which results in less stress and fewer stress concentrations. Other design features include a thicker bottom plate 104, heavy wall chord stubs 114 and lacing stubs 112, and intermediate suspension lugs 106 built into the box's side plates 108. The result is a simpler but stronger and heavier mast head box 110.

The disclosed device is a mast head assembly 100 for a dragline. The mast head assembly 100 comprises an elongated body 110 for connecting to a mast of a dragline. The elongated body 110 includes side plates 108 on opposite sides of the body 110. The side plates 108 have suspension lugs 106 for attaching cables from the mast head to the boom of a dragline. At least one of the chord stubs 114 is located above and to the rear of a first chord stub. Lacing stubs 112 are positioned on the side plates 108 so that the maximum stress in the mast head assembly 100 is where the chord stub 114 connects to the original chord 116. The highest remaining stress is located at the point where the upper/rear chord stub 114 connects to the original chord 116.

The upgrade design 100 improves the original design and should eliminate problems with machines that have frequent mast head cracking issues. The loading and deflections used in the analysis are worse than actually experienced by the mast head. The area with the shortest fatigue life for the original design lasted only 0.18 years, whereas the upgrade design 100 shows a shortest fatigue life of 3.57 years. This demonstrates a life increase of 19 times longer. Since the original design has lasted the customer 10-20 years, it is deduced that the upgrade 100 should last the life of the dragline. The increase in fatigue life is a result of a reduced max stress and a reduced stress range. The max stress for the original peaked at 80 ksi in the chord and lacing connection to the box, compared to 40 ksi for the upgrade 100. It should be noted that the max stress in the upgrade 100 is where the chord stub 114 connects to the original chord 116, and cannot be improved without changing the upper chord 116 near the tip of the mast. After studying the effects of thickening the wall of the chord 116 near the mast head box 110, it was determined that the best solution is to use the original chord 116, as a thicker chord wall creates a higher stress at the joint between the chord stub 114 and the bottom plate 104 of the mast head box 110.

An analysis was performed to compare the original design with feedback from the field, in order to develop an effective upgrade (e.g., mast head 100). Once the original analysis matched the problems reported from the field, the loads and boundary conditions were applied to the upgrade design 100. Based on results from a preliminary analysis, the upgrade 100 was then iterated to a final design to minimize stress, and provide a longer fatigue life.

After an initial analysis was performed on the original design, it was apparent that a beam analysis of the entire mast would be necessary to determine the displacements and rotations at the boundaries of the detailed analysis model. The beam analysis (see FIG. 9) was performed in Ansys. The detailed analysis (see FIG. 11) was performed in SolidWorks Simulation.

The beam analysis model of the entire mast was assembled using the VAX information from the original analysis of 1570W Lot 43, which has a very similar mast to Lot 45. The only difference between the Lot 43 and Lot 45 masts was one chord thickness that was adjusted for this analysis. The Lot 43 VAX information was exported to Excel, adjusted to the Lot 45 design, and then imported into Ansys from the Excel file. Ansys was able to take the information for each beam element, such as end points, cross sectional area, and material to build a 3-D stick model of the mast as shown in FIG. 9. When the analysis was complete, displacements and rotations were taken from the beam analysis model and mapped to the more detailed analysis models for the original and upgrade designs.

Both the original and upgrade detailed analysis models were designed as assemblies in SolidWorks (see FIGS. 1 and 2). The original design is slightly more complex due to the added stiffener plates, but the upgrade 100 has bent plates which added a degree of difficulty. The upgrade 100 was modeled using the original model, and removing the parts of the original that were no longer needed.

The mast head box 110, chords 116, and lacings 118 were modeled as one component for simplification of the meshing process (shown in FIGS. 1 and 2). The mast head pin hubs 102 were left in their original location, and the mast head box 110 was built up around them. The mast head pin 120 and lower main suspension links 122 were modeled as one component for simplification of the meshing, contact, and loading conditions (shown in FIG. 10). The mast head pin 120 and lower main suspension links 122 were simplified to create a better mesh. The mast head pins 120 are connected from the LH side to the RH side of the mast by a pinned connecting link 122. The connecting link 122 was represented by two rectangular pieces of plate as shown in FIGS. 10 and 14.

The first attempt at the mast head analysis used only the mast head box 110 and a very small portion of the mast chords, and lacing 118. The cut plane of the chords 116 was fixed, and the cut plane of the lacing 118 was given a symmetry constraint. This proved insufficient, and so an entire beam analysis of the mast was completed. Each location was given a displacement and rotation in each the X, Y, and Z direction. The upgrade model was constrained identically to the original model.

Once the beam analysis of the mast was completed, cut planes were taken to coincide with the boundaries of the detailed analysis model shown in FIG. 13. The cut planes may be at the elements shown in FIG. 12, and the displacements and rotations were taken at these points. Tables 1 and 2 (below) show the displacements and rotations resulting from the maximum and minimum load situations that were taken from the elements shown in FIG. 12.

TABLE 1 Cut Plane Nodal Displacements Mast Nodal Displacements (Max Load) Mast Nodal Displacements (Minimum Load) (Inches) (Inches) NODE UX UY UZ USUM NODE UX UY UZ USUM 977 −0.595 −3.212 0.021 3.266 977 −0.249 −1.376 0.008 1.398 1025 −0.693 −3.214 0.038 3.288 1025 −0.267 −1.376 0.016 1.402 1806 −0.934 −3.036 −0.032 3.177 1806 −0.371 −1.120 −0.012 1.180 1868 −0.880 −3.701 −0.032 3.804 1868 −0.349 −1.445 −0.011 1.487 2462 −0.756 −3.514 −0.011 3.595 2462 −0.303 −1.438 −0.003 1.470 2494 −0.825 −3.676 −0.023 3.768 2494 −0.329 −1.472 −0.008 1.508 2510 −0.859 −3.725 −0.032 3.823 2510 −0.342 −1.475 −0.011 1.514 2553 −1.257 −3.475 −0.015 3.696 2553 −0.517 −1.331 −0.007 1.428

TABLE 2 Cut Plane Nodal Rotations Mast Nodal Rotations (Max Load) Mast Nodal Rotations (Min Load) (Degrees) (Degrees) NODE ROTX (°) ROTY (°) ROTZ (°) NODE ROTX (°) ROTY (°) ROTZ (°) 977 −0.010 0.007 −0.078 977 −0.005 0.003 −0.010 1025 −0.011 0.001 −0.083 1025 −0.005 0.001 −0.011 1806 −0.008 0.000 0.389 1806 −0.003 0.000 0.184 1868 −0.004 −0.001 0.107 1868 −0.001 0.000 0.067 2462 0.054 −0.035 −0.058 2462 0.022 −0.013 −0.007 2494 −0.063 0.035 −0.015 2494 −0.025 0.013 0.013 2510 0.001 −0.002 0.062 2510 0.001 −0.001 0.045 2553 −0.020 0.008 0.287 2553 −0.010 0.004 0.138

The data from Tables 1 and 2 was then inserted into both the original and upgrade detailed analysis models as shown in FIG. 13.

Since the analysis assemblies were made of few components, only a few contacts are required to adequately setup the model. As shown in FIG. 14, there is a pinned contact that allows rotation but not translation to hold the connecting links 122 to the mast head pin 120. This method of connecting the two mast heads together accurately represents the real life mast head.

The mast head box 110 also has no penetration contacts setup between the round and flat surfaces of the pin 120 and the hubs 102. This allows the pin 120 to pull away from the hub 102, but does not allow the pin 120 to pass through the hub 102. Additionally, there is a 0.050″ gap between the face of the link hub and the face of the pin hub 102. This allows the pin 120 to pull towards the centerline of the mast until those faces contact each other. FIG. 14 shows the contacts for the original design. The contacts are identical for the upgrade design.

Two loading cases were used for this analysis. The max load case uses the highest load per suspension cable throughout any of the load cases and combines them into one conservative load case. The max load case values are taken from the original Lot 43 analysis. The minimum load case is actually the bucket on ground load case for the Lot 52 machine which has a different boom and mast angle, therefore creating a lower minimum load than actually occurs on the Lot 45 dragline.

By using a max load greater than the actual loads, and a minimum load less than the actual loads, a larger stress range is created for the fatigue analysis shown later. The maximum and minimum loads are shown in FIG. 15.

The beam analysis model has a very simple mesh. The elements are simple beam elements, with one element used to represent each piece of chord 116 or lacing 118. The element shapes are further defined by the cross sectional area, rotational inertia values, material properties, and other information provided within the original VAX analysis. The beam element mesh is shown in FIG. 16.

Mesh sizes and expansion ratios were applied as listed below:

Overall Mesh Size = 1.5″ Ratio = 1.5 Box Side Plates = 1″ Ratio = 1.5 Internal Plates = 0.75″ Ratio = 1.2 Gussets = 0.75″ Ratio = 1.1 Bottom Plate = 1.5″ Ratio = 1.5 Pin Hubs = 1.5″ Ratio = 1.5 Chord and Lacing = 1.5″ Ratio = 1.5 Chord to Bottom Plate = 0.5″ Ratio = 1.1 Intermediate Lugs = 1.5″ Ratio = 1.5

The mesh shown in FIG. 17 was created using SolidWorks Simulation's standard solid mesh. Four Jacobian Points were used, and the mesh was created at high quality with a tolerance of 0.075.″ More details are listed below:

Study name Study 3 (-Default-) Total nodes 756977 Total elements 406128 Maximum Aspect Ratio 61.228 Percentage of elements 79.6 with Aspect Ratio <3 Percentage of elements 0.1 with Aspect Ratio >10 % of distorted elements 0 (Jacobian) Remesh failed parts with in Off

Mesh sizes and expansion ratios were applied as listed below:

Overall Mesh Size = 2″ Ratio = 1.5 Box Side Plates = 2″ Ratio = 1.5 Internal Plate = 2″ Ratio = 1.5 Bottom Plate = 2″ Ratio = 1.5 Pin Hubs = 2″ Ratio = 1.5 Chord and Lacing = 1.5″ Ratio = 1.5 Chord to Bottom Plate = .25″ Ratio = 1.2 Intermediate Lugs = 1″ Ratio = 1.1

The mesh shown in FIG. 18 was created using SolidWorks Simulation's standard solid mesh. Four Jacobian Points were used, and the mesh was created at high quality with a tolerance of 0.075.″ More details are listed below:

Study name Study 2 (-Default-) Mesh quality High Total nodes 538567 Total elements 289125 Maximum Aspect Ratio 127.05 Percentage of elements 65.9 with Aspect Ratio <3 Percentage of elements 0.0529 with Aspect Ratio >10 % of distorted elements 0 (Jacobian)

The displacement plot in FIG. 19 shows that the tip of the mast has a significantly higher deflection than throughout the rest of the mast. This signifies that the chord pipes 116 should be heavier in this area. Since the deflection is high at this location, there will be significantly more weld cracks occurring here, and because this is where the mast chords 116 and lacing 118 connect to the mast head box 110, it is expected for those welds to eventually fail. Field experience has proven this expectation of weld failure at this location.

As shown in FIG. 19, the maximum displacement is 3.832 inches under the max load condition. FIG. 20 shows the deflection of the mast under the minimum load condition, with a max displacement of 1.521 inches.

The maximum stress location shown in FIG. 21 by the beam element analysis is in the same position as shown in the more detailed analysis models. This chord and lacing to mast head box connection is also where the most weld cracks occur in the field. FIG. 20 also shows that the upper chord 116 near the mast head box 110 is under high stress. Increasing the wall thickness on this section of the mast would reduce stress in the chord 116 and the weld that connects the chord 116 to the mast head box 110.

The results from the original design analysis match fairly closely with the actual failures that are experienced in the field. See FIGS. 22-24 for the high stress locations on the original design. Table 3 lists the max and min stresses (caused by the max and min loads) experienced at the 11 points denoted in FIGS. 22-24, and also provides comparison against the upgrade design 100.

One discrepancy between the original design analysis and the field feedback is the lack of stress at Point 8 in our analysis model.

The results from the upgrade design analysis show that the proposed design will greatly reduce stress in all of the areas of concern. See FIGS. 25-27 for the high stress locations on the upgrade design 100. Table 3 lists the max and min stresses (caused by the max and min loads) experienced at the points denoted in FIGS. 25-27, and also provides comparison against the original design 100.

It should be noted that locations 3, 8, 10, and 11 are not on the diagrams because those geometries have been removed from the upgraded design 100. The other points are located in the same places as on the original design for comparison purposes.

With the upgraded design 100 all of these high stress locations have been engineered to withstand the loads that are applied to the mast head box 110. As is evident from reviewing FIGS. 22-27, the stresses within the mast head box 110 and attachment points have been significantly reduced.

FIG. 25 shows that the chord and lacing connections to the box 110 have been greatly improved by adding heavy wall chord and lacing stubs 114, 112, 1″ blended weld radii, and by extending the mast head box 110 further down the mast. Also shown in FIG. 25 is point 5, which is the highest stress location within the upgraded design 100. This stress cannot be reduced any further without replacing a section of the upper rear mast chord 116. A separate study has been performed to determine the best size for the upper rear mast chord 116.

FIG. 26 shows the high stress locations in the walls 108 of the box 110. Notice that stress in the pin hub 102 is slightly higher than the stress in the wall 108 of the box 110. This is the ideal situation, because the contact stress created by the force of the pin 120 on the hub 102 is a non-avoidable force, and is within a safe stress range. Point 9 is also within a safe stress range, with the max stress in the plate material instead of a weld joint.

FIG. 27 shows that all of the internal box stresses have been eliminated with the improved geometry of the upgrade design 100. The picture shown is a section view of the mast head box 110, and directly compares with FIG. 24. Notice the reduced number of components, the clean design, and relatively low stresses within. Table 3 shows the results from both the original and upgrade finite element analyses. The table lists the maximum, minimum, and range of the stress, the Fatigue life calculation, and the life improvement ratio for each location shown in FIGS. 22-27.

The Life in years was calculated using the Life in cycles (B₁₀) divided by the number of cycles per year. The equation for Life in cycles (B₁₀) is below:

$B_{10} = \left( \frac{{Plate}\mspace{14mu} {or}\mspace{14mu} {Weld}\mspace{14mu} {Factor}}{{Stress}\mspace{14mu} {{Range}({ksi})}} \right)^{4.2}$

Because the loads used in the analysis were for extreme situations the fatigue life in years is much shorter than actual. For this reason, a Life Improvement Ratio was used. By taking the Shortest Life of any location for the original design and the upgrade design 100, the expected life improvement for the mast head was calculated in the last row of the table. The expected life improvement ratio is 19× the original life, which was approximately 10-20 years. The new design 100 can be expected to outlive the rest of the dragline.

TABLE 3 Fatigue Life and Stress Comparison Mast Head Analysis Fatigue Variables Weld Factor = 710 Exponential = 4.2 Plate Factor = 1050 Cycles per year = 447000 Origial Design Upgrade Design Max Min Stress Max Min Stress Life Location # Stress Stress Range Life Life Stress Stress Range Life Life Improvement See Doc. (psi) (psi) (psi) (cycles) (years) (psi) (psi) (psi) (cycles) (years) (ratio) Weld 1 79,129 31,676 42,453 86,035 0.19 35,941 14,309 21,832 2,625,347 5.87 30.49 2 80,204 32,101 48,103 81,313 0.18 28,825 11,873 16,952 6,494,670 14.53 79.87 3 51,845 20,816 31,029 532,697 1.15 Not Applicable - Geometry has been eliminated N/A 6 38,028 14,504 23,524 1,640,356 3.67 20,299 7,888 12,411 24,060,055 53.83 14.67 8 22,703 −2,500 25,203 1,227,954 2.75 Not Applicable - Geometry has been eliminated N/A 10  48,223 18,661 29,562 628,352 1.41 Not Applicable - Geometry has been eliminated N/A Plate 7 22,694 8,782 13,912 77,047,556 172.37 33,367 12,907 20,460 15,247,246 34.11 0.20 9 21,831 8,830 13,801 79,683,926 178.26 27,850 10,773 17,077 32,573,650 72.87 0.41 11  56,048 23,413 34,635 1,671,211 3.74 Not Applicable - Geometry has been eliminated N/A Mixed 4 69,360 27,438 41,922 144,887 0.32 26,968 10,530 16,438 38,232,206 85.53 263.88 5 40,296 16,261 24,035 7,752,642 17.34 38,775 16,103 23,672 1,597,711 9.57 0.21

The original design frequently experiences cracking at the top of the intermediate lug. The finite element analysis that was performed did not show a high stress at this location. There are two possible theories to explain this discrepancy.

One theory is that the ropes are oscillating at a much higher frequency than once per dig cycle, thus causing the plate to experience many more load cycles than the rest of the mast head box. This theory is perhaps part of the real issue, but is very difficult to analyze.

The second theory is that the stress range in the plate is larger than shown because of the potential for positive and negative stresses due to bending on the plate as the loads change within the upper and lower intermediate ropes.

The analysis was performed with the same boundary conditions and mesh as the original design, but the loads were changed in order to simulate various loads in the intermediate ropes. The loads used were the maximum and minimum loads used in the original analysis. However, they were switched so that the maximum Upper Intermediate load was combined with the minimum Lower Intermediate load, and vice-versa. This was an attempt to see if there was reversed bending occurring in the intermediate lug plate as the upper and lower rope loads vary throughout the digging cycle.

Load set 1: Main Suspension = Load set Main Suspension = 553 kips 2: 553 kips Upper Intermediate = Upper Intermediate = 131 kips 40.9 kips Lower Intermediate = Lower Intermediate = 49.2 kips 107 kips

The resulting stress plots are almost identical for the two load sets. However, another detail was observed. Instead of viewing only the Von Mises Stresses for the intermediate lug plate, the first (tension) and third (compression) principal stresses were viewed. FIG. 28 shows the first principal stress plot. The plot shows that the entire top edge of the plate is in tension as would be expected. However, when the third principal stress was plotted (see FIG. 29), the top edge had a small area experiencing compression stresses. What this means is that the stress range is larger than originally assumed when viewing only the Von Mises Stresses. When the minimum stress is changed from +8,320 (Von Mises) to −2,500 (Third Principal) for point 8, the fatigue life changes from 28.9 years to 2.75 years. This is a significant change in fatigue life.

This additional load case provides some explanation for why the intermediate lug plate has cracking issues, yet has a relatively low Von Mises Stress. The other explanation, which may compound the issue, is that there are many more cycles at this location due to the frequency of the ropes oscillating.

The highest remaining stress in the upgrade design 100 is located at the point where the upper/rear chord stub 114 connects to the original chord 116. The only way to improve this stress is to replace the original mast chord with a heavier walled chord. The purpose of this additional load case is to determine the wall thickness and length of replacement chord that would be required to successfully lower the stress at the connection joint.

All of the loads and boundary conditions were left at the maximum load situation, while the thickness of the chord 116 was changed to get the desired stress reduction. The heavy walled chord was extended to the joint where item 17 and 18 connect on drawing E004737. The runs that were performed are listed below.

Original Wall Thickness = Stub-Chord Stress = Stub-Plate Stress = 0.625″ 39.8 ksi 35.4 ksi Attempt 1 Wall Thickness = Stub-Chord Stress = Stub-Plate Stress = 0.75″ 35.1 ksi 37.3 ksi Attempt 2 Wall Thickness = Stub-Chord Stress = Stub-Plate Stress = 0.875″ 31.6 ksi 38.9 ksi

Attempt 2 had the lowest stress at the stub to chord connection. However, the original has the lowest stress at the stub to bottom plate connection. Based on the stress listed above, using the original chord 116 is the most favorable option for providing the longest fatigue life. FIGS. 30-32 show a comparison of the three runs.

Keeping the original 0.625″ chord wall will reduce the stress at the connection between the stub 114 and bottom plate 104 of the mast head box 110. This will keep the stress level to a comparable level at the stub to bottom plate connection.

The construction and arrangement of the mast head for a dragline, as shown in the various exemplary embodiments, are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. Some elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process, logical algorithm, or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed mast head for a dragline. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed mast head for a dragline. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. 

1. A mast head assembly for a dragline comprising: an elongated body for connecting to a mast of a dragline; said body having opposing side plates and chord and lacing stubs; said side plates having suspension lugs for attaching cables from the mast head to the boom of a dragline; said lacing stubs positioned on said side plates to provide structural stability; at least one of said chord stubs located above and to the rear of a first chord stub; wherein the highest remaining stress is located at the point where the upper/rear chord stub connects to the original chord.
 2. A mast head for a dragline comprising: an elongated body configured to connect to a mast of the dragline, the mast having at least one chord member and at least one lacing member; the body having opposing side plates, a top plate and a bottom plate, a suspension lug extending from each side plate and configured to receive cables supporting a boom of the dragline; a lacing stub disposed on at least one of the side plates and configured to connect with the lacing member; and at least one chord stub disposed on the bottom plate and configured to connect with the chord member.
 3. The mast head of claim 2, wherein the side plates are substantially parallel to one another, and the suspension lugs extend from the side plates in a substantially coplanar manner.
 4. The mast head of claim 3, wherein the suspension lugs are integral extensions of the side plates.
 5. The mast head of claim 3, wherein the suspension lugs each include an opening, and the openings are substantially axially aligned with one another.
 6. The mast head of claim 2, wherein each of the side plates include an angled portion that converge toward one another proximate the bottom plate to form a tapered region of the mast head.
 7. The mast head of claim 6, wherein the lacing stub is disposed on one of the angled portions.
 8. The mast head of claim 7, wherein the at least one chord member comprises a first chord member and a second chord member, and the at least one chord stub comprises a first chord stub and a second chord stub disposed on the bottom plate, and wherein the first chord stub is configured to connect with the first chord member and the second chord stub is configured to connect with the second chord member.
 9. The mast head of claim 8, wherein the at least one chord member further comprises a third chord member and a fourth chord member, and further comprising a second mast head having: an elongated body having opposing side plates, a top plate and a bottom plate, the side plates each having an angled portion that converge toward one another proximate the bottom plate, a suspension lug extending from each side plate and configured to receive cables supporting a boom of the dragline; a lacing stub disposed on one of the angled portions and configured to connect with another lacing member; and a third chord stub disposed on the bottom plate and configured to connect with the third chord member, and a fourth chord stub disposed on the bottom plate and configured to connect with the fourth chord member.
 10. The mast head of claim 2, wherein the lacing member and the chord member each have a longitudinal axis configured to intersect with one another at an intersection location, and wherein the elongated body substantially envelops the intersection location.
 11. The mast head of claim 2, wherein each side wall further comprises a hub formed therein, each hub being substantially free of support gussets.
 12. A dragline for mining, comprising: a boom; a mast having at least one chord member and at least one lacing member; and at least one mast head, comprising: an elongated body connected to the mast and having opposing side plates, a top plate and a bottom plate; a suspension lug extending from each side plate and configured to receive cables supporting the boom; a lacing stub disposed on at least one of the side plates and configured to connect with the lacing member; and at least one chord stub disposed on the bottom plate and configured to connect with the chord member.
 13. The mast head assembly of claim 1, wherein the side plates are substantially parallel to one another, and the suspension lugs extend from the side plates in a substantially coplanar manner.
 14. The mast head assembly of claim 13, wherein the suspension lugs are integral extensions of the side plates.
 15. The mast head assembly of claim 13, wherein the suspension lugs each include an opening, and the openings are substantially axially aligned with one another.
 16. The mast head assembly of claim 1, wherein each of the side plates include an angled portion that converge toward one another to form a tapered region of the mast head assembly, and wherein the lacing stub is disposed on one of the angled portions.
 17. The mast head assembly of claim 1, wherein the mast includes one or more chord members and one or more lacing members, wherein at least one of the lacing stubs is configured to connect with at least one of the lacing members and the upper rear chord stub is configured to connect with at least one of the chord members.
 18. The mast head assembly of claim 17, wherein the mast includes a first chord member and a second chord member, and the at least one chord stub comprises a first chord stub and a second chord stub disposed on the bottom plate, and wherein the first chord stub is configured to connect with the first chord member and the second chord stub is configured to connect with the second chord member.
 19. The mast head assembly of claim 17, wherein the lacing members and the chord members each have a longitudinal axis configured to intersect with one another at an intersection location, and wherein the elongated body substantially envelops the intersection location.
 20. The mast head assembly of claim 1, wherein each side wall further comprises a hub formed therein, each hub being substantially free of support gussets. 